Experiment: #11
Date: April 4, 2025
Title: Respiration
Aim: To investigate the use of oxygen in respiration
Materials:
● Yeast
● Bunsen Burner
● Water
● Spatula
● Methylene blue
● Measuring cylinder
● Glass tools
● Thermometer
● 4 beakers
● Sucrose
Method:
1. Heated some water in a beaker to 37°C.
2. Placed approximately 75 cm³ of this warm water into another beaker.
3. Added 3 spatulas full of sugar and three spatulas full of yeast to the beaker.
4. Stirred the mixture well for about 2 minutes.
5. Added a few drops of methylene blue to the mixture and stirred.
6. Continued adding and mixing until the mixture became pale blue.
7. Labelled the beaker as Beaker A.
8. Repeated the procedures for a second beaker, omitting the yeast and sugar.
9. Labelled this second beaker as Beaker B.
10.Left both beakers undisturbed for 30 minutes, observing occasionally.
11.Recorded the observations at the end of these 30 minutes.
12.Poured the contents of Beaker A into an empty beaker.
13.Repeated the pouring step several more times, pulling the hands further away each
time.
14.Repeated the pouring step for the contents of Beaker B into an empty beaker.
15.Included a table in the results.
Results:
Beaker
Start
After 30 minutes
Beaker A
Foam starts forming
Foam gets bigger
Beaker B
Absent
Absent
Discussion:
Beaker A showed foam formation, indicating that yeast was respiring and producing carbon
dioxide. The methylene blue faded, showing oxygen was used. Beaker B showed no change
because it lacked yeast and sugar. This confirmed that yeast needs sugar and oxygen for
respiration.
Source of error:
● Water was spilled for the beaker
Precaution:
● Pre-set the timer to ensure accurate timing.
● Handle the beakers carefully to avoid spilling.
Limitation:
● Only visual observation was used; no measurements of the volume of foam or
oxygen
Recommendation
● Yeast carries out respiration using oxygen, producing gas, which can be observed
through foam formation. Beaker B showed no activity because it lacked the
necessary components.)
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